docs: def map(self, key, value):
          """
          Args:
              key: Image name
              value: Image as jpeg byte data
  
          Yields:
              A tuple in the form of (key, value)
              key: Image name
              value: (image, faces) where image is the input value and faces is
                  a list of ((x, y, w, h), n)
          """
          try:
              image = self._load_cv_image(value)
          except:
              hadoopy.counter('DATA_ERRORS', 'ImageLoadError')
              return
          faces = self._detect_faces(image)
          if faces:
              yield key, (value, faces)